Detailed microphysics in a Lagrangian cloud model

The turbulent behaviour of clouds is responsible for many of the uncertainties regarding the timing and intensity of precipitation in weather and climate models. One of the fundamental problems here is that microphysical processes are essentially Lagrangian: they happen along trajectories of the flow (for small particles) or along fall trajectories (for bigger particles, influenced by the ambient wind). We have recently developed a new code, MPIC (moist parcel in cell), which deals with the dynamics of clouds in an essentially Lagrangian framework, i.e. by advecting parcels of fluid. Here, we propose to use the new MPIC model for studies of realistic atmospheric clouds and to couple the model to a bin microphysics scheme, where the amount of condensate associated with drops of different size categories is prognosed. This bin microphysics approach has previously been successfully implemented in the Met Office LEM, but is too computationally expensive for many applications where a high resolution is needed. The MPIC approach is particularly suitable for bin microphysics as a full size distribution can be advected by changing the coordinates of a parcel. This work will build on an existing collaboration with David Dritschel at the University of St Andrews.